1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor element such as a transistor which includes an oxide semiconductor, and a method for manufacturing the semiconductor device.
Note that a semiconductor device in this specification means all devices that can function by utilizing the semiconductor characteristics, and all of electronic optical devices, display devices and electronic appliances fall within the category of the semiconductor device.
2. Description of the Related Art
In recent years, a technique in which transistors are manufactured using an oxide semiconductor and used in electronic appliances such as electronic devices or optical devices has attracted attention. For example, a technique in which a transistor is manufactured using zinc oxide or In—Ga—Zn—O-based oxide as an oxide semiconductor and used for a switching element of a pixel of a display device, or the like is disclosed in Patent Document 1 and Patent Document 2.
A transistor including an oxide semiconductor is expected to considerably improve performance of a display device because such a transistor has higher field-effect mobility than a transistor including amorphous silicon.